Arousal

• Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception.
• It involves activation of the ascending reticular activating system (ARAS) in the brain, which mediates wakefulness, the autonomic nervous system, and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, desire, mobility, and readiness to respond.

Major neurotransmitter systems

Wakefulness is regulated by the ARAS, which is composed of projections from five major neurotransmitter systems that originate in brainstem and form connections extending throughout the cortex:

1. Noradrenergic system originate in locus coeruleus and ascends up into the neocortex, limbic system, and basal forebrain. Most of the neurons are projected to the posterior cortex which is important with sensory information, and alertness. The activation of locus coeruleus and release of norepinephrine causes wakefulness and increases vigilance. The neurons that project into the basal forebrain impact cholinergic neurons that results in a flood of acetylcholine into the cerebral cortex.
2. Acetylcholinergic system has its neurons located in the pons and in the basal forebrain. Stimulation of these neurons result in cortical activity and alertness. All of the other four neurotransmitters play a role in activating the acetylcholine neurons.
3. Dopaminergic system, released by substantia nigra. The neurons arise in the ventral tegmental area in the midbrain, and projects to the nucleus accumbens, the striatum forebrain, limbic system, and prefrontal cortex. The limbic system is important for control of mood, and the nucleus accumbens signal excitement and arousal. The path terminating in the prefrontal cortex is important in regulating motor movements, esp reward oriented movements.
4. Serotonergic system has almost all of its serotonergic neurons originating in the raphe nuclei. This system projects to the limbic system and the prefrontal cortex. Stimulation of these axons and release of serotonin causes cortical arousal and impacts locomotion and mood.
5. Histaminergic system in the tuberomammillary nucleus of the hypothalamus send pathways to the cerebral cortex, thalamus, and the basal forebrain, where they stimulate the release of acetylcholine into the cerebral cortex.

• All of these systems are linked and show similar redundancy. The pathways described are ascending pathways, but there also arousal pathways that descend. One example is the ventrolateral preoptic area, which release GABA reuptake inhibitors, which interrupt wakefulness and arousal. Neurotransmitters of the arousal system, such as acetylcholine and norepinephrine, work to inhibit the ventrolateral preoptic area.
• ARAS Activity is regulated by neurons that release the neurotransmitters acetylcholine, norepinephrine, dopamine, histamine, and serotonin.
• Activation of these neurons produces an increase in cortical activity and subsequently alertness.

• Arousal is important in regulating consciousness, attention, alertness, and information processing.
• It is crucial for motivating certain behaviors such as mobility, the pursuit of nutrition, the fight-or-flight response and sexual activity

Entities

• Consciousness altered
• Confusion
• Concentration difficult
• Disorientation
• Stupefaction

Miasms

JE, PLV, STLE, INFL, RBS, EEE/WEE, B19, HAV, VZV, YF